docs: def get_ceph_pool_sample(self, sentry_unit, pool_id=0):
          """Take a sample of attributes of a ceph pool, returning ceph
          pool name, object count and disk space used for the specified
          pool ID number.
  
          :param sentry_unit: Pointer to amulet sentry instance (juju unit)
          :param pool_id: Ceph pool ID
          :returns: List of pool name, object count, kb disk space used
          """
          df = self.get_ceph_df(sentry_unit)
          for pool in df['pools']:
              if pool['id'] == pool_id:
                  pool_name = pool['name']
                  obj_count = pool['stats']['objects']
                  kb_used = pool['stats']['kb_used']
  
          self.log.debug('Ceph {} pool (ID {}): {} objects, '
                         '{} kb used'.format(pool_name, pool_id,
                                             obj_count, kb_used))
          return pool_name, obj_count, kb_used